Power MOSFETs have been widely used in electronic devices due to fast switching speed, frequency performance, high input impedance, low driving power, and excellent temperature characteristics. A common trench-type power MOSFET device comprises a plurality of basic MOSFET cells. The space between the basic MOSFET cells has direct impact on the major parameters of power MOSFET including Drain-Source On-state Resistance (RDS(ON)). RDS(ON) is the total resistance of a unit area of the device between drain and source when the device is at on-state. RDS(ON) is an important factor for determining the maximum rated current and power loss of the device. A semiconductor wafer to fabricate trench MOSFETs is easily warped. When deep trench MOSFETs with high density are prepared on the semiconductor wafer, wafer warpage leads to a low product yield. This invention discloses solutions to reduce the semiconductor wafer warpage.